This invention relates to anti-theft alarm devices for video cassette recorders.
It is well recognised that video cassette recorders, particularly those in domestic residences, are prime targets for would-be thieves, and various alarm devices have been proposed heretofore with a view to preventing or deterring thefts of such machines. However, all known alarm devices suffer from one or more disadvantages.
For example, pressure mats have been provided to receive thereon video cassette recorders, such mats incorporating electrical circuits actuation of which is dependent upon the presence or otherwise of outside pressure on the mat. Thus, with the recorder in position on the mat, an alarm device associated with the circuit is deactivated because of the weight of the recorder. However, as soon as the machine is removed from the mat, the state of the circuit is altered and the alarm is activated. Such mats, as well as being clearly visible, rely for their operation upon the resiliency of the material of the mat which must be such as to effect a change in state of the circuit on removal of pressure therefrom. However the continuous presence of a heavy machine in one position on the mat cause compaction of the material of the mat such that the resiliency initially inherent therein is reduced or eliminated whereby the mat fails to operate on removal of the machine therefrom.
Further known anti-theft devices comprise housings for attachment to the body of the machine, said housings containing movement-sensitive switches which, on any displacement of the video cassette recorder from a normal rest position, are actuated to complete an electrical warning circuit. Such switches may be for example, mercury tilt switches or hydroswitches.
Alternatively, said housings may contain ultrasonic Doppler systems including transmitters and receivers so arranged that any interruption of the transmitted sound waves, be it by movement of the machine itself or as a result of the interference of a moving object remote from the machine, causes actuation of a warning mechanism.
It will be appreciated that the presence of all the above-detailed devices is readily apparent to a potential thief and he can himself take steps towards de-activating any such device--for example by disconnection from the supply of mains electricity or from the associated battery.